http://junkcharts.typepad.com/junk_charts/2012/05/spring-flowers-and-striking-hours.html

• … some charts are easier to read.
• we will be talking about why

Graphics consist of

• Structure (boxplot, scatterplot, etc.)
• Aesthetics: features such as color, shape, and size that map other characteristics to structural features

Both the structure and aesthetics should help viewers interpret the information.

• Cognitive aspects of perception and aesthetic choices
• Visual ordering mechanisms and color choices
• Faceting graphs to show additional variables

• pre-attentive: things that "jump out" in less than 250 ms (less than the time for a blink of an eye)
• Color, form, movement, spatial localization

Can you spot the odd one out?

nice applet by Chris Healey

• Color is stronger than shape

• Combination of pre-attentive features is usually not pre-attentive due to interference.

Can you spot the odd one out?

• Features in ggplot2 are called aesthetics

• main ones: colour, size, shape, alpha value

• … let's play with them a bit …

Find ways to improve the following graphic:

• Make sure the "oddball" stands out while keeping the information on the groups
• Hint: interaction combines factor variables

frame <- data.frame(x=runif(25), y=runif(25),
  g1=rep(c("A","B"), c(12,13)),
    g2=rep(c("1", "2"), c(13,12)))
qplot(x,y, shape=g1, colour=g2, data=frame, size=I(4))

• Hue: shade of color (red, orange, yellow…)
• Intensity: amount of color
• Both color and hue are pre-attentive. Bigger contrast corresponds to faster detection.

The exact same hue and intensity in one situation may appear to be a different color in a different context.

A and B are the same intensity and hue, but appear to be different.

Which is bigger?

• Position: higher is bigger (y), items to the right are bigger (x)
• Size, Area
• Color: not always ordered. More contrast = bigger.
• Shape: Unordered.

from ggplot2's online help

• Qualitative schemes: (not a lot more than 7 colors)

Quantitative schemes:

• use color gradient with only one hue for positive values

• use color gradient with two hues for positive and negative values. Gradient should go through a light, neutral color (white)
  

• Small objects or thin lines need more contrast than larger areas

R package based on Cynthia Brewer's color schemes ColorBrewer2.org

install.packages("RColorBrewer")
library(RColorBrewer)
help(package=RColorBrewer)
display.brewer.all()

• factor variable: scale_colour_discrete, scale_colour_brewer(palette=...)

• continuous variable:

scale_colour_gradient (define low, high values)

scale_colour_gradient2 (define low, mid, and high values)

• equivalent scales for scale_fill_XXX

• In the diamonds data, clarity and cut are ordinal, while price and carat are continuous
• Find a graphic that gives an overview of these four variables while respecting their types

data(diamonds)
qplot(carat, price, shape=cut, colour=clarity,
      data=diamonds)

• A way to extract subsets of data and place them side-by-side in graphics
• Syntax: facets = row ~ col Use . if there is no variable for either row or column (i.e. facets = . ~ col)

qplot(price, carat, data=diamonds, color=color,
      facets = . ~ clarity)

• The movies dataset contains information from IMDB.com including ratings, genre, length in minutes, and year of release.

• Explore the differences in length, rating, etc. in movie genres over time

• Hint: use facetting!